Aggregations

Do you remember that aggregations in SQL are used to compute a single result from a set of input values. Let's remind some common aggregation functions: COUNT, SUM, AVG, MAX, MIN.

At the same time, Aggregation in Django ORM is a powerful tool to perform calculations over query sets, enabling you to summarize or analyze data efficiently. It allows for operations like counting, averaging, summing, etc., across a set of records.

Basic Aggregation Examples

This query counts how many books each author has written.

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from django.db.models import Count
author_book_count = Author.objects.annotate(num_books=Count("books"))

Complex Aggregation

Finds the latest publication date for each author.

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from django.db.models import Max
latest_book_per_author = Author.objects.annotate(latest_publication=Max("books__publication_date"))

Aggregation with Filters

Aggregates the total pages of all books in the "Fantasy" genre.

python
total_pages_fantasy = Book.objects.filter(genre__name="fantasy").aggregate(Sum("pages"))